With the help of the newly-formed United Nations Intelligence Taskforce
(UNIT), led by their old friend Lethbridge-Stewart -- newly promoted to
Brigadier -- the Doctor, Jamie and Zoe discover that businessman Tobias
Vaughn has been conspiring with the Cybermen. Partially cybernised
himself, Vaughn plans to give the Earth over to the Cybermen unless the
Doctor can stop him... but the Cybermen have already arrived.

Production

In early 1968, while The Wheel In Space was
still in pre-production, Doctor Who producer Peter Bryant asked
Cyberman cocreator Kit Pedler for a new storyline featuring the metal
monsters. Pedler duly conceived a six-part adventure, apparently under the
title “Return Of The Cybermen”. As with all of Pedler's ideas,
it was agreed that another writer would be brought in to turn the
storyline into full scripts. This time, that task fell to story editor
Derrick Sherwin, who was commissioned to write them as The Invasion
on May 6th; the new title was intended to keep the appearance of the
Cybermen a secret. Permission for the staff contribution came
retroactively on July 8th.

In this instance, Bryant felt that there was not a lot of usable content
in Pedler's storyline. He suggested that Sherwin pare The Invasion
down to four episodes, and make only casual use of Pedler's concepts.
However, problems were quickly becoming evident on other forthcoming
serials -- including Paul Wheeler's “The Dreamspinner”, which
was intended to follow The Invasion into production -- and so the
decision was made to expand the Cyberman story to eight episodes, making
it the longest Doctor Who adventure since the twelve-part The Daleks' Master Plan two and a half years
earlier. The Invasion was scheduled as Serial VV, leading off
Doctor Who's sixth recording block. It would only be the third
story of Season Six, however, following both The
Dominators and The Mind Robber, which
were being held over from the previous block.

The Invasion would pilot a new
focus on adventures set on Earth in the modern day or the near
future

With the success of The Web Of Fear, Bryant
and Sherwin both felt that Doctor Who would be better served if its
focus was directed away from stories set in the far future or on alien
worlds, and was instead concentrated on adventures which took place on
Earth, in the modern day or the near future. The production team thought
that The Invasion could be used as a pilot of sorts for this new
vision; should it be successful, Doctor Who could then be retooled
for its seventh season with these ideas in mind. To this end, Douglas
Camfield, who had directed The Web Of Fear,
was brought on board to helm Serial VV.

Initially, it was thought that The Invasion might see the return of
Professor Travers and Colonel Lethbridge-Stewart, both of whom had
appeared in The Web Of Fear. In early May,
Camfield approached the characters' creators, Mervyn Haisman and Henry
Lincoln, to secure permission for their use. By the end of the month,
however, it was determined that the role for Travers was not significant
enough to merit the expense of hiring Jack Watling to reprise his role,
and the character of Professor Watkins was duly created as a replacement.
(Similarly, Isobel may have been a substitute for Travers' daughter,
Anne.)

Given that the elements established in The Invasion might be reused
in later stories, Bryant also considered the possibility of replacing
Lethbridge-Stewart with a character which would be wholly BBC-owned.
However, assistant head of copyright John Henderson noted that such a
character would still be the property of Haisman and Lincoln. Meanwhile,
it was decided that Lethbridge-Stewart should be promoted to Brigadier for
The Invasion, and that the character would now be the head of an
investigative military organisation. It appears that it was Camfield who
coined the name for this group: UNIT, the United Nations Intelligence
Taskforce. Meanwhile, it seems that the Cybermats -- the rodent-like
cyborgs which had appeared in both The Tomb Of The
Cybermen and The Wheel In Space --
were written out of The Invasion.

Lethbridge-Stewart, promoted to Brigadier, would now be
the head of an investigative military organisation: UNIT

With Sherwin busy writing Serial VV -- and, with increasing frequency,
sharing the producer's duties with Bryant -- his assistant, Terrance
Dicks, took over as script editor (the new name for the story editor
post) in July after Bryant himself had briefly filled in during June.
While working as a copywriter, Dicks had started making extra money by
writing for the radio. He soon switched to radio full-time and then moved
to television, earning credits on series such as The Avengers and
Crossroads.

Meanwhile, on April 30th, Frazer Hines had been contracted for Serials VV
and WW; with the abandonment of “The Dreamspinner” on April
9th, the latter was now intended to be Dick Sharples' “The
Amazons”. Hines informed Bryant that he intended to leave Doctor
Who after these two stories, as he and his agent felt that it was time
for Hines to take advantage of the popularity he had garnered during his
two years on the programme. Hines' departure was announced to the press on
September 5th.

Around the middle of August, however, Patrick Troughton also decided that
Season Six would be his last on Doctor Who and told Bryant that he
would remain on the show until the following spring. He was now finding
the Doctor Who production schedule to be extraordinarily gruelling,
and was worried that he would become typecast as the Doctor. Troughton
then asked Hines to stay on Doctor Who for the same length of time
so that the two actors could depart together. Hines' father had recently
passed away as well, and consequently Hines was now more reticent to give
up his Doctor Who salary. Although his agent still wanted Hines to
leave the show as planned, the actor agreed to Troughton's request.

Pre-production on The Invasion continued throughout the summer. A
significant contribution was made by costume designer Bobi Bartlett, who
opted to introduce a new appearance for the Cybermen. The most substantial
change was to the creatures' helmets, with Bartlett building up the left
and right sides in a sort of “earmuff” motif. Camfield,
meanwhile, was successful in securing considerable involvement from the
Ministry of Defence, who appreciated that Sherwin's script portrayed the
military in a positive light. The Ministry promised the use of facilities,
vehicles, equipment and troops for the serial.

The performer originally cast as Corporal Benton was
dismissed for chronic tardiness

Amongst the cast selected by Camfield was John Levene, who was intended to
play a Cyberman, as he had done on The
Moonbase. The actor's resume also included several other walk-on
parts, including Z Cars, Adam Adamant Lives!, and a Yeti for
Camfield on The Web Of Fear. For The
Invasion, however, Levene -- whose real surname was Woods -- found
himself given the opportunity to tackle a somewhat meatier role when the
performer originally cast as Corporal Benton was dismissed for chronic
tardiness. Camfield reallocated the part to Levene. Camfield also cast his
wife, Sheila Dunn, as both the International Electromatics computer voice
and the telephone operator.

Filming began on August 31st, with model work at the Ealing Television
Film Studios. An unprecedented location shoot lasting nearly two weeks
followed, during which Camfield himself made an on-camera appearance as
the car driver. The first three days were all spent at venues in
Gloucestershire. Things got off to a faltering start on September 3rd when
the helicopter intended for use at RAF Fairford proved unavailable due to
insurance problems. The same day, cast and crew moved to Williamstrip Farm
at Coln St Aldwyns. The scenes in the field where the TARDIS lands were
filmed there and on nearby Hatherop Road on the 3rd and 4th. September 5th
was spent at Kingston Minerals in Kempsford, which served as the IE
compound.

For the scenes on the roof of the IE offices, the Associated British
Malsters' Guinness factory in Wallingford, Oxfordshire was used on the
6th. For the offices themselves, Millbank Tower in London filled in, with
filming there occurring on the 7th. A number of London locations were
employed on September 8th and 11th for the Cybermen's invasion of the city
and UNIT's battle against them. The scenes at Watkins' house were also
filmed on the latter day, at St James' Gardens in Kensington, as was more
IE compound material at the Guinness Brewery in London. In between, on the
9th and 10th, and afterward on the 12th, a number of other IE compound
sequences were shot at TCC Condensers in Ealing. Finally, the scene of the
Doctor and Jamie in the canoe was filmed on September 13th at Lisson Grove
before the lift shaft material was enacted at Ealing Studios. On an
unknown date, the helicopter scenes which had been abandoned at RAF
Fairford were remounted at the Denham Aerodrome in Buckinghamshire.

Douglas Camfield had hoped to film the Cybermen marching
near Tower Bridge, the Houses of Parliament and Hyde Park

Unfortunately, despite the length of the location shoot, things had not
gone to plan. Time had been lost on a number of sequences, particularly
the various street scenes which were hampered by passers-by. This meant
that Camfield was unable to shoot at several London landmarks in addition
to St Paul's Cathedral; he had hoped to film the Cybermen marching near
Tower Bridge, the Houses of Parliament and Hyde Park. Camfield was also
forced to omit the action scene in which UNIT recaptures Professor Watkins
in episode six. The script was rewritten to have Packer report the events
verbally to Vaughn. A scene in which Gregory is killed by the Cybermen in
the sewers also had to be inserted into the same episode, because the
character was originally shot by Benton during the battle.

Although many of the latter episodes of the fifth production block had
enjoyed recording at the BBC's Television Centre, the new block saw
Doctor Who return to Lime Grove Studio D. All eight episodes of
The Invasion were recorded there, on consecutive Fridays from
September 20th. Two weeks later, on October 4th, Wendy Padbury enjoyed a
week's holidays as Zoe did not appear in part three. Unusually, episodes
five and eight were recorded largely out of sequence, with Camfield opting
to record all the scenes on a given set before moving on to the next; the
same approach was used to a lesser extent for episode seven. For part
eight, taped on November 8th, it was Hines' turn to get a week off --
Jamie only appeared in the final scene, which had been filmed on
location.

During recording, Bryant approached Courtney about returning to Doctor
Who on a regular basis the following year; the actor agreed without
hesitation. Already, Bryant and Sherwin were formulating plans for a very
different Season Seven -- one in which the Brigadier and the UNIT
organisation would feature very heavily.

The Invasion was the final Doctor Who serial to feature the
contributions of Kit Pedler. Pedler went on to develop the ecological
thriller Doomwatch with former Doctor Who story editor and
Cyberman cocreator Gerry Davis. In the early Eighties, he conceived
Mind Over Matter for Thames Television. Shortly thereafter, Pedler
suffered a heart attack and passed away on May 27th, 1981.